In the oil and gas industry, subsurface formations are investigated by well logging tools. Such well logging tools can be used to determine formation characteristics. In many cases, acoustic logging tools are used to measure formation acoustic properties, which may be used to derive other characteristics of the formations. For example, acoustic logging tools can be used to image a borehole wall and identify fractures within the borehole wall.
Such acoustic logging tools may include acoustic transducers for transmitting an acoustic signal into a formation and for receiving acoustic signals that return from the formation. The return signal can be used to generate an image of the formation.
A common problem encountered with such acoustic logging tools is that the tools do not adequately focus and image formations at short standoff distances between the borehole wall and the transducer. This is particularly problematic in logging-while-drilling operations where the standoff distance between the drill collar and the borehole wall can be very small.